Acoustic measurements using currently available tools and methods provide key information in oilfield borehole logging. The currently available acoustic tools are useful in providing a wide range of information regarding the surrounding formation and the borehole parameters. Surface seismic and vertical seismic profiling (VSP) methods are utilized to provide imaging of the overall geological structure of a hydrocarbon reservoir. Sonic and other well logging methods provide good resolution imaging in the immediate vicinity of the borehole. Sonic imaging is yet another technique that bridges the gap in spatial resolution between these seismic and well logging methods.
Some tools include a single source of sonic waves and two or more receivers, however, most of the tools now include two or more acoustic sources and many receivers arranged in an array. A primary use of acoustic borehole measurements is the estimation of compressional (P) wave and/or shear (S) wave formation slowness. The estimation of compressional and/or shear wave formation slowness is often expressed as an ST (slowness vs. time) plane, and can be visualized at the wellsite with current technology.
The assignee of the present application, Schlumberger, has developed a wireline sonic imaging tool (referred to as the Borehole Acoustic Reflection Survey (BARS) tool) that allows reservoir features such as reflectors and fractures to be imaged.
While sonic imaging generally has been successful, waveform data acquired for sonic imaging purposes typically contain many types of arrivals in addition to the desired reflected arrivals, such as tool-borne noise and borehole-borne noise. For example, direct compressional and shear headwaves and tube waves, which are a part of the raw data that are acquired during downhole acoustic measurements, tend to obscure the reflected arrival waves relating to acoustic reflectors in subterranean formations. As a consequence, often it is not evident at a wellsite whether or not the acquired acoustic measurements include the desired reflected arrival data relating to subterranean acoustic reflectors. Techniques that effectively identify or eliminate this noise are desirable in the acquisition and processing of sonic imaging data. Moreover, techniques that are capable of indicating possible acoustic reflectors in subsurface formations on the fly for real-time, wellsite decision-making are clearly desirable.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems outlined above. Accordingly, an object of the present disclosure is to provide improved systems and methods for processing acoustic waveform data acquired in a borehole in which reflected arrival waves are easily identified and selected from tool-borne and borehole-borne arrivals. A further object of certain embodiments herein is to provide improved systems and methods that use real-time indicators or imaging of possible acoustic reflectors in subsurface formations for adjusting data acquisition parameters at, for example, the wellsite. A further object of certain embodiments herein is to provide indicators or imaging of possible acoustic reflectors in subsurface formations for enhanced data processing at, for example, a data center by reducing the overall time that is required for processing acoustic waveform data.